Wireless communication systems are well known in the art. Generally, such systems comprise communication stations which transmit and receive wireless communication signals between each other. For network systems such as mobile cellular systems, there are typically two types of communication stations, namely, base stations which provide access to the network infrastructure and wireless transmit/receive units (WTRUs) which conduct wireless communications with the base stations. Networking between WTRUs without network base stations, known as ad hoc networking, is also known in the art.
There is a growing dependence upon wireless communications in the home, office, and when traveling. It is not uncommon for a user to have several different WTRUs such as different home, office, and mobile wireless telephones. There is a need to replace the use of multiple WTRUs with a single WTRU which can be used in the home, office, or when traveling.
In many commercial networks, a network of base stations is provided wherein each base station is capable of conducting multiple concurrent wireless communications with appropriately configured WTRUs. Some WTRUs are configured to conduct wireless communications directly between each other, i.e., without being relayed through a network via a base station. This is commonly called peer to peer wireless communications.
One type of wireless system, called a wireless local area network (WLAN), can be configured to conduct wireless communications with WTRUs equipped with WLAN modems that are also able to conduct peer to peer communications with similarly equipped WTRUs. Currently, WLAN modems are being integrated into many traditional communicating and computing devices by manufactures. For example, cellular phones, personal digital assistants, and laptop computers are being built with one or more WLAN modems. Accordingly, there is an increasing need to facilitate communications among such WTRUs with WLAN modems. For instance, it would be desirable if a first user of a PDA equipped with a WLAN modem could share data, such as a phone book, with a second user having a cellular phone equipped with a WLAN modem locally without going through a telecommunications network.
A popular wireless local area network environment with one or more WLAN access points, i.e., base stations, is built according to the IEEE 802.11b standard. The wireless service areas for such WLANs may be restricted to specified well defined geographic areas known as “hot spots”. Such wireless communication systems are advantageously deployed in areas such as airports, coffee shops, and hotels. Access to these networks usually requires user authentication procedures. Protocols for such systems are not yet fully standardized in the WLAN technology area, since the IEEE 802 family of standards is evolving.
There are two prevalent ways to implement wireless communications in WLAN and other networks: 1) an infrastructure mode; and 2) an ad-hoc mode. FIG. 1A illustrates an infrastructure mode, where WTRUs conduct wireless communications via a base station 54 that serves as an access point to network infrastructure 16. The base station 54 is shown as conducting communications with WTRU 18, WTRU 20, WTRU 22, WTRU 24 and WTRU 26. There are no direct intercommunications between the WTRUs illustrated in FIG. 1A. The communications are coordinated and synchronized through the base station 54. Such a configuration is also called a basic service set (BSS).
Infrastructure mode can provide an Extended Service Set (ESS) that is a set of two or more BSSs forming a single sub network. Many corporate WLANs require access to a wired local area network (LAN) for services such as file servers, printers, and Internet links, and they operate in an infrastructure mode.
In contrast to infrastructure mode, ad hoc mode does not normally use the network infrastructure. Ad hoc mode operates with peer to peer communications and is also called “independent BSS.” In ad-hoc mode, two or more WTRUs establish a communication among themselves without the need of a coordinating network element, i.e., a base station. Ad hoc mode operation is illustrated in FIG. 1B where WTRUs 22, 24, 26 are communicating without a connection to a network base station.
In ad-hoc mode, access points to network infrastructure are not required. However, a base station can be configured with the ad hoc protocols to act as the other WTRUs in peer to peer communications. In such a case, a base station may act as a bridge or router to another network or to the Internet. Where a base station does join an ad hoc network, it is treated as another WTRU and does not normally control the flow of communication. For example, FIG. 1B illustrates base station 54 in communication with WTRU 18 and WTRU 20 in an ad hoc network. In this scenario, the base station 54 does not control the flow of data.
Communications are normally limited to the other stations in an ad hoc network, but one WTRU may communicate indirectly with another WTRU via a third WTRU. For example, as shown in FIG. 1B, where both WTRU 22 and WTRU 24 are communicating in ad hoc mode with WTRU 26, communications may occur between WTRU 22 and WTRU 24. Additionally, when a WTRU is in ad hoc mode, it typically ignores infrastructure mode base station transmissions. It is also necessary for one WTRU to initiate ad hoc mode and other WTRUs to join in. The other stations will assimilate the operating parameter information as they join the ad hoc network.
The station that starts an ad hoc network selects the ad hoc network's operating parameters, such as the service set identifier (SSID), channel, and beacon timing, and then transmits this information in, for example, beacon frames. As stations join the ad hoc network, they assimilate the operating parameters. In infrastructure mode, parameters such as the SSID are normally specified by a network controller connected to network base stations.
The SSID in an IEEE 802-based system can be a 32-character unique identifier attached to a header of packets sent over a WLAN. The SSID then acts as a password when a WTRU attempts to connect to a BSS or an independent BSS. The SSID differentiates one WLAN from another, so all base stations and all devices attempting to connect to a specific WLAN normally use the same SSID. A device will not normally be permitted to join a BSS unless it can provide the unique SSID.
In an IEEE 802-based system, once more than one station is part of an ad hoc network, all of the stations share the burden of sending beacon frames by a random distribution of that task to each station. Algorithms such as the spokesman election algorithm have been designed to “elect” one device as a master station, i.e., a pseudo base station, of the ad hoc network with all other stations being slaves.
In lieu of using a different WTRU in each different environment, it would be advantageous to have a WTRU personal communicator capable of switching from one type of network to another without a loss of connectivity. For example, a mobile WTRU communicating with or seeking to communicate with a target WTRU may travel into areas of poor signal quality where the communications with a particular network that serves the target WTRU becomes sporadic or nonexistent. In such cases, it would also be desirable if the WTRU can switch to a different network or a peer to peer communication to relay communication through another WTRU which is in direct contact with a target WTRU or a network through which a target WTRU can be reached.